The paper presents results on the preparation and study of the structure, optical and electrochromic properties of sol-gel derived thin films Of WO3, MoO3, and mixed films on based upon these. The films were deposited in a simplified sol-gel process. Raman spectra results showed that WO3 and the mixed films were predominantly amorphous, while crystallization of the MoO3 films was detected. All films showed an electrochromic effect. Color efficiencies were in the range 58 to 100 cm(2)/mC for a wavelength of 550 nm, reaching a value of 130 cm(2)/mC for the WO3 film. The results confirm that the simple sol-gel process which has been developed is promising for low cost applications in electrochromic smart windows.